Disaster with billions of ash trees in America and Europe: East Asian emerald worm

We've seen disasters on an ecosystem scale in the past, when an invasive species was introduced into an area where it had no natural enemies. These species will grow explosively and kill a wide range of native organisms.

In 2018, China faced an epidemic of cicadas, while hair clippers invaded and killed a series of cherry trees in Japan. In Australia, a single feral cat can slaughter a whole colony of seagulls, while the country has up to 2 million cats roaming.

Emerald beetle.

Most recently, a small and beautiful insect that is only found in Northeast Asia has found its way to the US and Europe. There it created a nightmare for the ash tree, a symbol of many Western cities and countryside.

This is the story of the emerald worm's westward journey

What we know about this killer creature is from 1860, when a priest, French naturalist Armand David found it in Beijing, China.

He brought this emerald worm to France, where an entomologist named Léon Fairmare wrote the first short description of it, published in the journal Revue d'Entomologie in 1888.

It is a beetle, iridescent green, about 8.5 mm long, 1.6 mm wide. Scientists give it a nomenclature, Agrilus planipennis. But with its distinctive appearance, this species is often called the emerald worm or jade beetle.

The emerald beetle is a species native to Northeast Asia, including parts of Russia, Mongolia, China, Japan and Korea. They only specialize in chiseling and eating ash leaves.

When female jade beetles lay eggs in the bark of ash trees, their eggs develop into larvae, with a life span of up to 500 days. During this time, jade beetle larvae will burrow deep into the ash stem, forming hollows, preventing water and nutrients from going up from the roots to feed the stem. The ash tree will eventually drop its leaves, die, and rot.

Over millions of years of evolution, native ash species have thus developed many forms of resistance to these worms, including secreting chemicals such as tannins to repel them. Northeast Asia also has many species of natural enemies that kill emerald worms, especially an Asian wasp that lays parasitic eggs on jade beetles, killing them from the inside.

With these delicate balances of nature, native emerald worm populations cannot thrive and ash populations in those countries are also protected. Things only got complicated when the emerald worm found its way west to America and European countries.

Larvae of the emerald beetle.

 They only specialize in chiseling and eating ash leaves.

In 2003, a population of jade beetles was found in Moscow. From 2003 to 2016, this beetle has continuously spread westward, the European Union countries at a rate of 40 km per year. In 2019, a population of emerald worms spread from Russia to Ukraine. It is expected that by 2036, this beetle will colonize central Europe.

And that's a disaster, because European ash populations are very vulnerable to this worm. They have not yet developed effective mechanisms against the emerald beetle. Immediately after appearing in Denmark, jade beetles have infected up to 90% of the ash in this country. The absence of natural enemies such as the Asian wasp also causes the population of emeralds to thrive and wreak havoc.

In 2016, a study published in the journal Ecology even predicted that the emerald beetle could lead to the extinction of the ash across Europe. The price of ash is therefore tending to increase when the supply of quality wood is decreasing day by day.

The loss of ash will also affect 1,000 species of organisms around the ecosystems it supports, including 12 species of birds, 55 species of mammals and 239 species of vertebrates.

"More than 100 species of lichens, fungi and other insects that depend on ash are likely to decline or become extinct if the ash goes extinct as well," said Peter Thomas, a PhD student at Keele University in the UK. . "The landscape of the UK countryside will henceforth change forever".

Jade beetles can wipe out ash in 6,000 metropolitan areas in the US.

In the United States, ash is now grown in urban areas, contributing an important landscape and thermoregulatory function to cities. However, the same story in Europe is playing out in the North American continent. The ash here is also endangered because of the emerald beetle.

This insect was first officially identified in Michigan in 2002. But American scientists predict that they may have entered the US since the 1980s. Despite being geographically separate from Northeast Asia, but Emerald beetles can enter the US via sea, on cargo ships.

These ships are usually built in wooden crates of ash. And if the wood is still fresh, the emerald beetle larvae can still survive in it, until they reach the US. Here, the insect also finds an environment with no natural enemies, with no Asian wasps, and the American ash trees are completely resistant to the emerald beetle.

In Europe, because jade beetles are slow-moving and naturally diffuse, many of the ash species there have developed some resistance to the insect, although not as effectively as in Northeast Asia. But jade beetle was brought into the US suddenly, making the resistance of ash in the US almost zero.

As a result, once again, where the emerald beetle went, the pine trees fell. Statistics show that this insect has killed millions of ash trees in the US. And it will continue to kill 1.4 million trees over the next 30 years. This is enough to wipe out 100% of the frequency in 6,000 US metropolitan areas.

The hottest spots include New York, Chicago and Milwaukee, which are rich in ash and are on the verge of emerald beetle invasion.

A dying ash tree on a US street.

The further in cities, the more damage caused by emerald beetles, because that is an area that lacks natural enemies of insects, such as woodpeckers. "Many urban areas grow only one species or genus of ash, leading to the easy spread of exotic insects," says ecologist Frank Koch at the US Forest Service's Southern Research Station. said.

As a result, when the ash trees fell, the city would have to replant new trees. The damage that this tiny bug causes to the United States can be up to 30 million USD per year. In the worst-case scenario, that number could reach $4.9 billion between now and 2050.

Authorities in the US are trying to find ways to kill the emerald beetle, from cutting infected trees, using insecticides to releasing natural enemies. However, these measures did not prevent but only slowed the rate of spread of the emerald beetle to half that of Europe.

In the United States, each year this insect still invades at a speed of about 20 km, threatening the existence of 8.7 billion ash trees across North America.

An ash tree was wrapped in plastic and cut down because of an emerald beetle infection.

Nevertheless, "the results of this study provide a wake-up call for cities that are monocropping a single species of tree for their landscapes," says computational ecologist Emma Hudgins at McGill University in Canada. ".

Trees in urban environments provide many benefits such as improving air quality, cooling streets, capturing carbon, providing habitat for wildlife, and improving mental and physical health. of citizens.

So, the lesson learned here is that to keep cities green and sustainable, urban planners should plant a variety of trees and avoid monocultures of a species that is susceptible to pests and diseases. especially European and North American ash.